Induction furnace load control



n 25, 1946- .H. A. STRICKL AND, JR

INDUCTION FURNACE LOAD CONTROL Filed March 2, 3 Sheets-Sheet l w.) ME

W JW s am/.2

ATTORNEY June 25, 1946. N H. A. STRICKLAND, JR 2,402,852

INDUCTION FURNACE LOAD-CONTROL ATTORNEY Patenterl- June 25, 1946INDUCTION FURNAQELOAD CONTROL Harold A. Strickland, In, Detroit, Mich.,as

slgnor, by mesnc assignments, to Budd Wheel Company, a corporation ofPennsylvania Application March 2, 1943, Serial No. 477,749

furnaces, and more specifically to induction furnaces adapted to heatbillet or bar stock for forging purposes. In such furnaces it mayreadily occur that due to various causes such as power failure to thecontrol circuits, or operation of limit switches within the inductionfurnace control or by direct or accidental stoppage of the heating cyclecircuits, the timers controlling the heating cycle of the furnace arereset. Consequently, if a new heating cycle is instituted withoutremoval of a partly heated billet, the furnace may be damaged by meltingof the billet.

It is, therefore, an outstanding object of the present invention toprovide an induction furnace control requiring complete removal of aworkpiece from the furnace in which the normal heating cycle has beeninterrupted. Another object is to prevent reheating of a workpiece aftera normal heating cycle without first completely removing the workpiecefrom the furnace. An additional object is to provide furnace controlmeans for preventing overheating or melting of a workpiece. An objectalso is to prevent oper ation of an induction heater unless theworkpiece is completely inserted in the furnace.

The above and other objects are 'efiectuated by the mechanism andprocedures hereinafter de scribed and illustrated in the accompanyingdrawings, in which Fig. 1 is a side view of a furnace embodying theinvention;

Fig. 2 is a rear elevational view showing details of the switchoperating mechanism;

Figs. 3, 4, and 5 are diagrammatic views showing the workpiece entering,partly entered, and fully entered into the furnace chamber;

Fig. 6 is a wiring diagram of the electrical circuits; and

Fig. '7 is a section ofthe apparatus shown in Fig. 2.

The general physical arrangement of the furnace follows that of my copending application Serial No. 384,503, filed March 21, 1941, on whichthis invention is an improvement. r isdisclosed in said application andas shown in Fig. l, the furnace includes an upright rear section 80formingan L-shape with a front lower section it, the section if)containing control apparatus and, section ii, capacitors l2.

Placed closely in the angle of the L-shape is the furnace unit l3 havinga casing i a ventilating screen 85. hood switch box is and hood or doorH. In dotted outline within-the'casing 9 Claims. (01. 219-13) ll areshown the heating coil l8, heating chamber l8. mouthpiece 20, c-bracketfurnace supports 22, and bus bars 23 having depending connections to thebus framework 25 and power inlet connection 26 in section II. Furnacesection [0 includes the ejector rod 30 extending into the furnacechamber as shown in Fig. 3, ejector collar 3|, bell crank arms 32 and 33on pivot 34, bell crank spring 35, bell crank cam 36, limit switch 31,bell crank arms '38,'bell crank rod 39 and full load limit switch 40,these elements being mounted on the partition plate 9, separating thefurnace section III and 13.

At the right hand base of furnace section H is illustrated a footlever4|, pivoted at 42, which on actuation against tension of spring 43,compresses fluid in a servo-motor M thereby transmitting pressurethrough pipe line 35 to the floating fluid pressure piston-cylinder unit86 shown in Figs. 2 and 7. The cylinder has pivotal connection to thebracket 8! to which the depending hell crank spring 35 is also attached.The piston of unit to is pivotally connected to the hell crank arm sothat on extension of the piston on pressure of foot pedal ii the bellcrank 32-33 is rotated to move the ejector rod into the fur ace chamberiii, thus forcing outwardly the con tained workpiece. Simultaneously thelimit switch hell crank arms will follow collar 36 due to spring loadingas will now be more fully described.

Reference is made to Fig. 2 for further structural details relative tothe load switch operating mechanism. in this figure it appears that thepivot pin lid for the pedal operated ejector hell crank 322-33 alsosupports hell crank cam it with its associated arm Elli and arm 3%.While bell crank lit-3t is an integral unit, the position of cam 36 inthe -35 hell crank unit is adjust= able to control the point ofoperation of switch 3?, this switch having a normally open switchcontact element Bio and a normally closed switch contact element ilh.

As shown more clearly in Figs. 3-5, the earn element 325 has a circularperiphery 5i ternil mating in a recess 52? on the far side from thefurnace chamber. Adapted to move over the cam periphery is the switcharm 53 terminating in the arm roller lid. When the roller rests inrecess 52 the limit switch li'l is in its open position. Rearwardmovement of the cam away from the furnace will lift the arm roller outof recess 52 thus closing switch contact element 31a and opening till).This movement is opposed by coil 3 spring I, attached to arm The bellcrank arm II of the bell crank unit H! is fixed relative to arm 50, andat its end has pivotal connection to the rod 39 extending upwardly to apoint adjacent load limit switch III. This switch has an arm Iiicarrying at its end a fitting 5!, vertically apertured to receive theend of the upstanding bell crank rod 39. The arm BI is pivotally mountedon the fitting 58 so that movement or the fitting on the rod operatesthe switch 40. A collar 51 is adjustably fixed to rod II at apredetermined distance from the lower rod pivot such that when the bellcrank I048 is moved to its extreme rearwardposition the collar 51 willhave engaged the fitting BI and moved the arm of switch 40 to closedposition. At the other positions of hell crank movement the switch II isopen, as appears from Figs. 4 and 5.

Figs. 3, 4, and 5 show diagrammatically the relative position of furnaceand load limit switch mechanism. The switches and controls are mountedon the rear of back plate 9 in operative relationship with the electorrod 30 and the attached rod collar II. On the front of back plate 9 theejector rod 3! extends into furnace chamber ll, substantially axiallythereof, and is thus adapted to contact with the bar 60 or otherworkpiece inserted through the furnace mouth 20. Adjacent and below themouth is the single pole double throw load limit switch Ii having switchcontact elements "a and 8ib and also having a sprkig controlledoperating arm 62 and roller arm terminal 63, this terminal being adaptedto engage yieldingly the work-piece while it is being inserted removedfrom the furnace chamber. This engagement is such as to cause opening ofthe normally closed switch element B In closure of the normally openswitch contact element Bib only when the switch arm I! is forceddownwardly by the workpiece the spring moving the switch arm to positionto close Bio and open Bib as soon as the load moves out of contact withroller ll.

Having in mind the physical arrangement of furnace and switch elements,as shown in Figures 3 to 5 particularly, the operation is as follows.Prior tointroduction of the workpiece all load switch contact elementsexcept 31b and Uia are in open position. Upon engagement of theworkpiece with the arm of load switch 6i, as shown in Fig, 3, contactelement Bib is closed and lid is opened. Further movementof the bar tothe position of Fig. 4 brings about engage-' ment of bar and ejectorrod, thus moving out collar 3| to rotate cam 38 and close switch contactelement 31a and open 31b. In the final position of mg. 5, with the barfully within the furnace chamber, cam rod 39 is at its uppermost po.sition thus closing the switch 40. At the same time the mouth switch IIis freed of workpiece zagement and lb switch element is opened and inclosed. It may be here observed that if the workpiece element lib closedwhen the workpiece is at the rear chamber fere with the successfuloperation of the furnace.

Having described the physical features of the invention it remains todescribe the electrical circuits, through the functioning of which theswitches are controlled so as to require complete removal of a workpiecein case of accidental power stoppage due to causes within or wit o thefurnace circuits.

is over-long so as to keep switch 4 The wiring diagram is shown'in Fig.6, the power source supplying alternating current being I indicated atill, and the mainline-s at H and l2.

The circuits may be roughly classified in five sections designated assupply, starting, load safety, timer and high frequency and identifiedin the drawings as A, B, C, D, and K, respectively. The supply section Aincludes fuses I3, overload disconnecting heaters and main switches".

Included also are the main 60 cycle pilot lamp 16, water pressureswitches 11, water pressure pilot lamp [8, water heater l9, and waterthermostat 80.

Main lines H and 12 extend from the supply circuit A into the startingand load protective circuits B and C, these two sections being mutuallydependent for operation. Starting circuit B is based on a pilotcontactor relay li which on energization is adapted to close itsswitches 82 and 83. In addition to the basic elements mentioned thestarting circuit includes the hood switches 84 and 85, pilot lamp 86 andmain contactor relay switch 81, the circuit passing from main line 72through tap line 5, pilot lamp 86 and relay 8| in parallel, main relayswitch ll, pilot lamp relay contact 83 and hood switch 84 in parallel,and hood switch 85 to the load safety section C. Also from hoodand pilotrelay switches 83 and 84 a branch line leads through pilot relay switch82 to a sequence or distributor switch II, which selects the particularfurnace of a bank of furnaces for energization, and thence to the timercircuit section D.

limit, such closure will not inte'r- The basic elements ofthe'lOBd-Sitffity section V C are the anti-reset relay 8! and switchcontact elements 37a, 31b, and am, no. Anti-reset relay 89 is adapted onenergization to open the normally closed anti-reset relay switches IIand 92.

In addition to the enumerated basic elements there is included in the Csection the anti-reset pilot lamp 96, and water temperature and flowswitches I00 and iii. The circuit leads from main line ll through watertemperature and fiow coil 89 and pilot lamp 88 in parallel to a commonJunction I02,- thence by anti-reset relay switch 9| to a common junction"II. From point )3 the circuit leads through switch contact elements Biband 31b to point M2.

The timer current section D is formed principally of two timers of anyappropriate commercial make together with related elements. The functionof the timer is to effect a time limit, sublect to adjustment, on theamount of heat received by the workpiece and two timers are used toinsure completion of a heating cycle in case one timer should fail toperform properly. Timer I it includes the timer solenoid ill, motor H2and magnetic timer lock switch iii. Associated with this timer are thetimer on-relay ill and timer on-relay switch I II. A switch for themotor ill and the relay ill includes a contact arm H6 which is movableto an on contact element H1 and to an 03" contact element III. 8lmilarly in timer III) is included the solenoid III. motor I22, andmagnetic lock switch ill. Asso- 'ciated with this timer I20 are timeron-rela I, timer on-relay switch I25, and contact arm m movable to oncontact element I21 and "oi!" contact element ill. The timer section Dalso includes the hood solenoid I28 for operating the hood latch, andhood pilot lamp I80 for indicating completion of the heating cycle.

The timer circuit is traced from the sequence selector switch 88 throughparallel lines III and I82, including timer solenoids III and I2Irespectively, to the main line I2. power after opening of sequenceswitch 88, tap lines are connected at points I88 and I84 on lines IIIand I82 respectively at points between the sequence switch 88 andsolenoid coils III and I2I respectively, these tap lines leading throughthe timer switches II8 and I28 respectively and a common return line I88to point I04 between B and C sections. Line I88 also supplies power tothe timer switch arms I I8 and I28. The timer onrelay coils H4 and I24are connected to the main line I2 from points intermediate the on timercontact elements I I1 and I21 and the corresponding motor. The hoodsolenoid connects the main line I2 to the ofl" timer contact elements H8and I28. Associated with timer section D is the main contactor relay I Hwith the heat-on pilot lamp I42 connected in parallel therewith. Circuitconnections with the timer section are made by extension of timercircuit I85 from tap point I31 through load switch 40, furnace paneldoor switches I88 associated with various side or rear panel doors,on-relay timer switches I25 and H5 to tap point I40 at the relay I4I.Also the main line I2 is extended from tap point I48 through tap pointI88 and hood switch I44 (in the switch box I8) to the main contactorrelay I4I. A pilot iamp'I48, indicating complete insertion of theworkpiece, connects the power side of the panel door switches I88 withthe main line I2.

There remains to be described the high-frequency section E. This sectionincludes the main contactors relay contacts and a rectifying circuit forsupplying direct current for operation of the high frequency contactoroperating coil. There are two main contactor relay switches I50, I SIand the previously mentioned switch 81 in the starter section B, alsooperated by the contactor relay.

The rectifying means is embodied as a conventional bridge I52 comprisingfour branches I58, I84, I85 and I58 with copper oxide or equivalentelements inserted, one in each branch, with such polarity as to producea direct current potential at tap points I51 and I58, as indicated.Alternating current is led to tap points I58 and I80 on the rectifierfrom main line I2 at tap point I38 and from the C-Dline I85 at a tappoint I8I, the resultant tap line'including in series a resistancecut-in combination of a resistance I82 and normally closed by-passswitch I88 on the resistance, and the main contactor relay switch I5I;The rectified circuit connects in series the main contactor relay switchI80 and the high frequency contactor operating coil I84. Energizationoi' magnet coil I84 closes the switch I88 of the high frequency highvoltage circuit I88 including the power source, I81, capacitor I88(corresponding to I2 previously mentioned) and heating coil I8. Usuallythe power source provides current at about 800 volts and 3000 cycles inthe heating circuit.

Having in mind the complete organization with associated electrical andmechanical features, the operation of the furnace control follows. Theside and rear panel doors are closed closing panel door switches I88.The water cooling system is turned on, this resulting in closureofpressure To maintain switch 11 and flow switch Ill. The main switches IIare then closed, current flow being indicated by the various currentflow indicating lamps I8, 18 and 88. Illumination of lamp 88 indicates aclosed circuit through anti-reset relay 88, by way of normally closedload switch contact elements 8Ib and 81b. Simultaneously, anti-resetrelay switches 8I and 82 are closed thus locking the anti-reset relayclosed and conditioning the circuits for application of voltage on thestarter section B and timer section D on introduction of the workpiece.

The workpiece is now inserted in the furnace chamber causing the closureof load switch contact element 8Ib and thereby applying voltage to pointI04 and starter section B and timer section D.

Before the workpiece has passed completely over load switch arm roller83, it engages the ejector rod 80, thus actuating the arm of load switch81. This switch has two contact elements 81a and 31b which aresimultaneously actuated, switch contact element 31a serving on closure,to maintain a voltage on the starting and timing circuits irrespectiveof the action of load switch 8|. Opening of either or both 81b or 8Iashifts the anti-reset relay circuit entirely through antireset relayswitch 8| so thatshould the power be withdrawn from this relaypermitting opening of the switch 8|, it cannot again be closed unlessboth load switch contacts 81b and 8Ia are closed, this requiringcomplete unloading of the furnace.

The workpiece is now moved to the rear end of the furnace chamberclosing load switch 40 in the timer D section. The furnace hood is thenclosed bringing about closure of hood switches 85 and I44, and amomentary closure of hood switch 84. On the closure of hood switches 85and 84, a closed circuit is at once established through normally closedmain contactor relay switch 81 and the pilot contactor relay 8| with itsassociated lamp 88. 'Ihereupon the two pilot contactor relay switches 82and 83 are closed, switch 88 locking the pilot relay 8| closed sincehood switch 84 is closed only momentarily during the hood closingmovement. Also power is applied by way of switch 82 to the sequenceswitch 88.

The system of circuits is now conditioned for initiation of a heatingcycle. This will develop when the sequence switch 88 which controls thesequence of power application in the furnace bank are already closed,power is at once supplied from circuit point I04 between sections B andC through line I 85. and from main line I2 to the main contactor relayHI and its associated signal lamp I42.

The energization of relay I4I closes main contactor control relayswitches I58 and I5I, and opens switch 81 in the starting sectioncircuit. The effect of opening switch 81 is to deenergize pilotcontactor coil 8i and cause the opening of I pilot contactor relayswitches 82 and 88, thus breaking the circuit through the sequenceswitch. Additionally, closure of main contactor relay switch I5I closesa circuit from point IN on power line I35 through the resistance cut-inswitch I83 to point I89 on the rectifier bridge I", thus, applying avoltage at point I68 from main line 12, creating a direct currentvoltage at points I81 and III which is effective through closed switchI88 to energize the high-frequency contactor coil I84. Thereupon, theswitch I85 in the main induction heating coil circuit are closed andpower from the source I8! is applied to heating coil II.

On completion of the heating cycle either timer contact arm breakscontact at I" or. I21 and opens relay switches H or I25, thusdisconnecting relay I II and opening the main circuit and stopping theapplication of power. In addition, timer contact arms 8 and I28 engagecontact elements I I8 and I28 causing functioning of hood solenoid I29to open the furnace door and hood switches 88 and I. The workpiece maynow be removed from the furnace by actuation of foot pedal ll andapplication of tongs.

An outstanding feature of the described system has already been referredto, namely, the impossibility of reinstituting the heating cycle, oninterruption of the cycle due to limit switch operation because of dropin cooling water pressure or temperature or control power failure.Should any one of these conditions develop, and the workpiece remain inthe furnace, the anti-reset relay coil 89 would be de-energized thusholding switch 82 open and preventing the re-application of voltage onthe timer section. In order, therefore, to continue furnace operation itis necessary to remove the billet, bar or other work-: piece completelyfrom the furnace in order to reset the anti-reset relay. It is thenobvious to the operator that the workpiece has already been fully orpartially heated and thus the likelihood of reheating of partiallyheated bars to the fusion point with resulting damage to the furnace andloss of time and material is avoided.

On normal operation it is impossible to recycle the equipment withoutcompletely removing the workpiece from the furnace because it isnecessary to remove control voltage from the timers to reset them andthis can only be done by opening both load switch contact elements 31aand 8 I b which due to their mechanical arrangement require the completeremoval of the workpiece- It is observed further that in the describedcontrol it is necessary to move the bar or other workpiece completelywithin the furnace to the rear end thereof before the heating cycle cancommence. This is due to the necessity of closing load switchAdditionally it is pointed out that the hood switch I, movable to closedposition only on lowering of the hood I1, prevents the main contactorrelay from functioning when the hood is open and also automaticallybreak the main contactor relay circuit when the hood is opened.

In operation the described system and apparatus work effectively andpositively accomplishing diversified results with a relativelysimplified arrangement. Obviously, some modification may be made in thedetails of the system and structure, and hence the scope of theinvention should be read from the appended claims.

What is claimed is:

1. In electrical heating apparatus, a heating coil adapted to receiveand heat a workpiece, switch means for inducing a heating cycle in saidcoil on insertion of said workpiece, and means for in :venting a renewedheating cycle in said coil after failure and re-establishment of powerand prior to complete removal of said workpiece from 80 before heatingpower can flow.-

8 the coil, said means including a workpiece operated switch mechanismin operative relation with said coil at each end thereof.

2. In electrical heating apparatus, a heating coil adapted to receiveand heat a workpiece. switch means for inducing a heating cycle in saidcoil on insertion of said workpiece, and means for preventing a renewedheating cycle in said coil after failure and re-establishment of powerand prior to complete removal of said workpiece from the coil, saidmeans including at least two switches, and plural means actuated by theworkpiece for operating said switches, one of said switch actuatingmeans being adjacent the coil end.

3. An induction heating coil having a hollow heating chambersubstantially closed at one end, and adapted to receive a load, pluralswitches. load .pperated switch means adjacent the open end of saidchamber adapted to operate one of said switches, and load operatedswitch means intermediate the chamber ends adapted to operate another ofsaid switches, a control circuit connected to said switches forenergizing said heating coil, and relay means connected in parallel withsaid switches effective to prevent reenergizing of said heating coilafter an initial heating period and prior to complete removal of theload from said switch means.

4. In electrical heating apparatus, a heating coil adapted to receiveand heat a load, power mains, switch means connected to said mains foropening and closing the circuit of said coil, timer means connected tosaid switch means for timing the heating cycle, a starting control meansconnected to the timer means and load safety means connected to thestarting control means for preventing re-heating of said load. withoutcomplete removal of the load from said coil, said load safetymeans'including a switch operated by the movement of the'load into andout of said coil.

5. In electrical heating-apparatus, a heating coil adapted to receiveand heat a load, power mains, switch means connected to said power mainsfor opening and closing the circuit of said coil, timer means connectedto said switch means for timing the heating cycle, a starting controlmeans connected to said timer means, and load safety means connected tosaid starting control means for. preventing re-heating of said load.without complete removal of the load from said coil, said load safetymeans including plural switches connected across said means and switchoperating means positioned at each end of said coil and adapted forseparate operation at entry and full insertion of the load within saidcoil to prevent re-heating of the load prior to complete removalthereof.

6. In electrical heating apparatus, a heating coil adapted to receiveand heat a load, switch means for opening and closing the circuit ofsaid coil, power mains, timer means for timing the heating cycle, astarting control means, and load safety means for preventing re-heatingof said load, without complete removal of the load from the said coil,said load safety means comprising a relay coil and a relay contactnormally open when the relay coil is deenergized connected in seriesacross said mains, load switches connected in parallel with said relaycontact and normally closed on removal of load from said heating coil,and additional load switches normally open on removal of load from saidheating coil operatively connected to said closed switches andelectrically connected to one of said power mains,

for closure or opening of said closed switches, said relay contact beingadapted for closure on the energization of the relay coil, and saidclosed switches to open and open switches to close on the insertion ofload within said heating coil, the closing of said open switches by theload, conditioning the timer means for closure of the heating coilcircuit.

7. In electrical heating apparatus a heating coil for heating aworkpiece, and load safetycontrol means for requiring complete removalof the v for operating one each of said closed and open,

switches.

8. In electrical heating apparatus, a heating coil for heating aworkpiece, and load safety control means for requiring complete removalof the workpiece after a partial or complete heat treatment thereofprior to additional heating, said means comprising power mains, twoswitches is free of load connected in parallel around said contactwhereby on application of power, the relay coil is energized to closeand lock said contact, and load operated means effective at one end, andat a point intermediate the ends of the heating coil to close one ofsaid open switches and open one of said closed switches, whereby onopening of the contacts power cannot be .reestablished in said relaycoil prior to complete removal of said load.

9. In electrical heating apparatus, a heating coil adapted to receive aworkpiece, switchmechanism for establishing current flow in said coil oninsertion of a workpiece therein, and means for preventing a renewal ofcurrent flow in said coil after cessation of current flow therein andprior to removal of said workpiece from the coil, said means including aworkpiece operable switch in operative relation to said coil at thepoint adjacent that of full workpiece insertion.

HAROLD A; STRICIUJAND, JR.

